Technology has evolved to allow the drilling of wells to depths approaching 8,000 meters. At those depths the tools that are deployed have to resist rupture or collapse forces that are orders of magnitude higher than the original depths for which such tools were designed. At the same time space restrictions in such applications do not allow for simply scaling up the dimensions of all components to resist the heightened burst and collapse loads that could be encountered. The new conditions dictate a new approach to the tool to meet the often conflicting parameters of higher pressure differentials and limited space. Individual components that in old designs see increased differential pressure stresses now need to be rethought as to shape and placement in the tool to make the tool function reliably in a new high depth environment. While the ultimate mission of a tool may be unchanged, such as using hydrostatic pressure with the addition of pressure from the surface into an annulus to set a tool such as a packer, the configuration of the tool has to change to handle the new parameters that come into play from ultra-deep deployments of such tools.
The present invention is illustrated using an example of an existing tool discussed below and shown in FIG. 1 with a redesigned tool for deep applications shown in FIG. 2a-2b. While the context for the illustration of the inventive concept is hydrostatically operated tool actuators, the scope of the invention will be understood by those skilled in the art to be found in the appended claims.
FIG. 1 shows a model SB-3H Hydrostatic Setting Tool/Packer currently offered by Baker Hughes Incorporated of Houston, Tex. The packer has slips 3 that move out radially by riding up on cones 5, 16. In between the cones 5, 16 there is a seal assembly that is longitudinally compressed so that it extends radially in a well known manner. The seal assembly includes components 7 through 14 as illustrated in FIG. 1. A lock ring assembly 18, 19 holds the set position that is not shown. A stop ring 2 acts as a backup to the assembly of shifting pistons 23 and 39. When the pistons 23 and 39 are unlocked for movement toward the stop ring 2, the packer is set in the known manner.
In order to actuate, pressure in the annulus either rises to a predetermined value with depth or is raised to a predetermined value from the surface to break rupture disc 45. When that happens, the chamber between seals 33, 34 and 35 on one side and seals 30, 31 and 43 on the inside builds pressure on the piston 44 that initially traps the locking dog 41 to the mandrel 1. Dog 41 extends through a window in piston 39 and into an aligned groove in the mandrel 1 so as to keep piston 39 from moving until a recess on release piston 44 aligns with dog 41 to allow dog 41 to come out radially so that the piston 39 is no longer locked. The pressure that enters the chamber between seals 33, 34 and 35 on one side and seals 30, 31 and 43 on the inside then propels the piston 44 against the piston 39 for tandem movement as shear pin 40 breaks. Note that the driving force for piston 44 is the annulus pressure entering chamber 100, after the rupture disc 45 is broken, on one side and atmospheric pressure trapped in chamber 102 on the other side. Note also that the locking components for the piston 39 are in the atmospheric chamber 102. Chamber 104 is also initially at atmospheric pressure so as to put piston 39 initially in pressure balance to annulus pressure and to the opposed atmospheric chambers 102 and 104 acting in opposing direction.
Initially, piston 39 overlays dogs 38 to prevent movement of piston 23. Piston 23 is subjected to an unbalanced force with exposure to the annulus at its lower end near dogs 38 and exposure to atmospheric pressure from chamber 106 acting in opposition. Movement of piston 39 to liberate dogs 38 allows the unbalanced pressure on piston 23 to move uphole in tandem with piston 39 to set the packer in the manner described above.
While the above described design functioned well for moderate depth of about 5,000 meters the design incorporates features that at 8,000 meters or more would cause component failure making the device inoperable. One of the issues with the present design is the quantity of the net force that has to be retained by a lock assembly when any of the pistons is subjected to an unbalanced force before setting. The greater depths just magnify this force level causing the locking system to be more robust or to be subject to failure. However, the design also features not only a locking system for each piston but also location of at least a part of the locking system inside atmospheric chambers. At greater depths the differential pressures on atmospheric chambers are magnified forcing the components to be thicker walled structures to resist collapse or burst pressures. However, there is also the issue of lack of space in a borehole at depths of 8,000 meters and more that makes a locking system located in an atmospheric chamber problematic.
The present invention presents several unique and independent approaches to actuation tools triggered by hydrostatic or/and applied pressure in an annulus. One approach is to put multiple pistons in pressure balance to annulus pressure. Another is to move the locking mechanism from outside any atmospheric chamber. Yet another is to use a single locking mechanism for all the pistons and to reduce the loading on such a locking mechanism by using pressure balanced piston. The use of a single lock for all the pistons reduces component redundancy leaving space to make components thicker to handle the expected differential pressure loads at depths in excess of 8,000 meters. These and other features of the present invention will be more readily apparent from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the literal and equivalent scope of the appended claims.